#include <bits/stdc++.h>
using namespace std;

// #define int long long
#define rep(i, n) for (long long i = (long long)(0); i < (long long)(n); ++i)
#define reps(i, n) for (long long i = (long long)(1); i <= (long long)(n); ++i)
#define rrep(i, n) for (long long i = ((long long)(n)-1); i >= 0; i--)
#define rreps(i, n) for (long long i = ((long long)(n)); i > 0; i--)
#define irep(i, m, n) for (long long i = (long long)(m); i < (long long)(n); ++i)
#define ireps(i, m, n) for (long long i = (long long)(m); i <= (long long)(n); ++i)
#define SORT(v, n) sort(v, v + n);
#define REVERSE(v, n) reverse(v, v+n);
#define vsort(v) sort(v.begin(), v.end());
#define all(v) v.begin(), v.end()
#define mp(n, m) make_pair(n, m);
#define cout(d) cout<<d<<endl;
#define coutd(d) cout<<std::setprecision(10)<<d<<endl;
#define cinline(n) getline(cin,n);
#define replace_all(s, b, a) replace(s.begin(),s.end(), b, a);
#define PI (acos(-1))
#define FILL(v, n, x) fill(v, v + n, x);
#define sz(x) long long(x.size())

using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vs = vector<string>;
using vpll = vector<pair<ll, ll>>;
using vtp = vector<tuple<ll,ll,ll>>;
using vb = vector<bool>;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

const ll INF = 1e9+10;
const ll MOD = 1e9+7;
const ll LINF = 1e18;



vll G[2005];

vll dfs(ll v, ll p){
  vll res(1,1);
  for(auto nv: G[v]){
    if(nv==p) continue;
    auto tmp=dfs(nv,v);
    ll n=res.size();
    ll m=tmp.size();
    vll nres(n+m-1);
    rep(i,n) rep(j,m){
      (nres[i+j]+=res[i]*tmp[j]%MOD)%=MOD;
    }
    res=nres;
  }
  res.push_back(1);
  return res;
}

signed main()
{
  cin.tie( 0 ); ios::sync_with_stdio( false );
  ll n,k; cin>>n>>k;
  rep(i,n-1){
    ll a,b; cin>>a>>b;
    G[a].push_back(b);
    G[b].push_back(a);
  }
  
  if(k==0){
    cout<<1<<endl;
    return 0;
  }
  
  auto v=dfs(0,-1);
  cout<<v[k]<<endl;
  
}